JPH03419B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a vulcanized foam rubber composition comprising a crystalline diene rubber, a liquid diene rubber, a vulcanizing agent, and a blowing agent. Conventionally, in the rubber industry, particularly in the footwear industry, materials made by foaming rubber have been used for various purposes. By foaming rubber, it has become possible to add several new functions such as weight reduction and cushioning, and it is now being used to take advantage of these functions. Conventionally, various rubbers such as natural rubber, styrene-butadiene copolymer rubber, and ethylene-vinyl acetate copolymer have been mainly used as raw materials (base materials) for such foams. However, foams made using these rubbers have the drawbacks of complicated processing and poor weather resistance, and when ethylene-vinyl acetate copolymer is used, the foams have poor elasticity and abrasion resistance. Questions such as sufficiency arise. In contrast, it has been found that foams with excellent processability can be obtained by using crystalline diene rubber such as 1,2-polybutadiene as a raw material (base material), and it has come to be widely used. . However, even in such excellent foams, some drawbacks are recognized. The drawback is that after vulcanization and molding, the foam undergoes significant shrinkage due to heating. Due to the large shrinkage, dimensional stability deteriorates, making it impossible to obtain highly accurate products. For example, when used in footwear, if the shrinkage is large when bonding the bottom and upper parts of the foam, the resulting footwear product will be deformed and distorted, leading to a high incidence of defects. The present inventor has completed the present invention as a result of intensive studies to solve the above-mentioned drawbacks in order to take advantage of the characteristics of foams made of crystalline diene rubber. That is, according to the present invention, crystalline trans-1,4-polyisoprene rubber or 1,2-polybutadiene rubber having a melting point of 50 to 110°C,
By blending a liquid diene rubber, a vulcanizing agent, and a blowing agent, a vulcanized foam rubber composition can be obtained that has excellent processability, excellent performance when formed into a foam, and less shrinkage upon heating. In the present invention, the crystalline diene rubber has a melting point of 50 to 50, taking into consideration processability and foam performance.
Trans-1,4-polyisoprene and 1,2-polybutadiene at 110°C are used. If the melting point of the crystalline diene rubber is lower than 50°C, kneading workability will be poor. Also, if the temperature is higher than 110℃, kneading must be performed at a high temperature.
This causes problems such as scorch and poor foaming, and also causes insufficient fluidity during molding, impairing the properties of the resulting foam. Note that the melting point here is a term commonly used in the field of polymer chemistry, and specifically means the value obtained by measurement with a differential calorimeter. Further, the degree of crystallinity is preferably 5% or more, preferably in the range of 5 to 50%. The molecular weight of the above crystalline diene rubber is 60,000~
400,000, particularly preferably in the range of 100,000 to 300,000. If the molecular weight is too small, the viscosity of the composition will be too low, resulting in poor workability and poor molding processability when unvulcanized. On the other hand, if the molecular weight is too large, the fluidity of the composition will deteriorate, resulting in a decrease in moldability and poor foaming of the foam, which is undesirable. In the present invention, as the liquid diene rubber, low molecular weight polymers or copolymers of diene compounds such as butadiene, isoprene, and 1,3-pentadiene can be used. Specific examples thereof include liquid polyisoprene rubber, liquid polybutadiene rubber,
Examples include liquid pentadiene rubber, liquid butadiene-isoprene copolymer rubber, liquid butadiene-pentadiene copolymer rubber, and liquid isoprene-pentadiene copolymer rubber. Among these, liquid rubbers containing at least 10 mol % of isoprene, such as liquid polyisoprene rubber and liquid butadiene-isoprene copolymer rubber, are preferred from the viewpoint of processability and physical properties of the foam. These liquid diene rubbers may be copolymerized with a small amount of a vinyl compound such as styrene or acrylic acid as long as the gist of the present invention is not impaired. Furthermore, a compound having a functional group such as a carboxyl group, an acid anhydride group, a hydroxyl group, an isocyanate group, or an epoxy group may be added to the molecular chain or at the end thereof. The liquid diene rubber mentioned above preferably has a vinyl bond content of 35% or less. Vinyl bond amount
If it exceeds 35%, processability will be poor and the performance of the final foam will be reduced. The amount of vinyl bonding is more preferably 20% or less. In addition, the amount of vinyl bonds or the amount of cis-1,4 bonds referred to herein means the amount measured by infrared absorption spectrography. In addition, the above liquid diene rubber has a molecular weight of 6000.
~100000, especially in the range of 15000 to 60000. If the molecular weight is too small, the foaming of the foamed rubber composition and the physical properties after vulcanization will be poor; if it is too large, the composition will have poor fluidity, and furthermore, it will be difficult to prevent shrinkage due to heating when it is made into a foam. I end up not being able to do it anymore. In addition, the molecular weight here refers to the viscosity average molecular weight. Such a liquid diene rubber can be produced by various methods, but it is particularly preferably produced by an anionic polymerization method. Among them, metallic lithium,
Alternatively, a living polymerization method using organolithium such as methyllithium, propyllithium, butyllithium, or distyrenyllithium as a catalyst makes it possible to easily control the molecular weight and generate a microstructure with a small amount of vinyl bonds, and also allows copolymerization. Since the combined process is easy to manufacture, it is preferably employed. Although it is preferable to use a polymerization solvent because it facilitates the control of polymerization, there is no problem even if it is not used depending on the case. Examples of polymerization solvents that can be used include hydrocarbons inert to the reaction, such as n-butadiene, isopentane, n-hexane, n-heptane, benzene, toluene, and xylene. In the present invention, the weight ratio of crystalline diene rubber and liquid diene rubber is preferably in the range of 97/3 to 40/60 (crystalline diene rubber/liquid diene rubber).
used in Especially considering workability, it is more preferable that the weight ratio is in the range of 95/5 to 50/50. In the present invention, the vulcanizing agent used is one commonly used in the rubber industry, such as sulfur, peroxide or quinone dioxime. Among them, sulfur is preferably used. There is no particular restriction on the amount of the vulcanizing agent used, and it is used within the range normally used in the rubber industry, but considering the performance of the foam obtained from the composition of the present invention, crystalline diene rubber It is preferably used in an amount of 0.1 to 20 parts by weight, particularly 0.5 to 10 parts by weight, based on 100 parts by weight of the total amount of liquid diene rubber. In the present invention, any blowing agent that is commonly used in the rubber industry can be used without any problem, but representative examples include inorganic blowing agents such as sodium bicarbonate and ammonium carbonate, N,
Examples include organic blowing agents such as N-dinitropentamethylenetetramine, azodicarbonamide, and benzenesulfonyl hydrazide, and preparations containing these as main ingredients. It is also possible to use a foaming aid such as salicylic acid or a urea compound together with these foaming agents. There is no particular limit to the amount of blowing agent used, and it may be determined according to the expansion ratio of the desired vulcanized foam rubber composition, but it is usually 100 parts by weight in total of the crystalline diene rubber and liquid diene rubber. 0.05~
It is preferably used in an amount of 20 parts by weight, particularly in the range of 0.1 to 10 parts by weight. The vulcanized foam rubber composition of the present invention is produced by mixing a specific crystalline diene rubber, liquid diene rubber, vulcanizing agent, and blowing agent using a suitable mixer. Examples of the vulcanized foam rubber composition of the present invention include natural rubber as described in JP-A-50-151246, cis-1,4-polyisoprene rubber, styrene-butadiene copolymer rubber, polybutadiene rubber, etc. Solid rubber, thermoplastic polymers such as styrene-isoprene copolymer, ethylene-vinyl acetate copolymer, polyethylene, polypropylene, etc. may be blended, and fillers and activators used in ordinary rubber compounding may also be blended. , tackifier resin, zinc white, stearic acid, anti-aging agent, vulcanization accelerator and other rubber compounding chemicals may be added without any problem. The vulcanized foam rubber composition of the present invention is made into a foam by vulcanization accompanied by foaming (for example, press vulcanization). The foam thus obtained is suitable for use in footwear such as shoe soles, as well as in cushioning materials, vibration-proofing materials, sound-absorbing materials, heat-insulating materials, packing materials, sealing materials, buoyancy materials, and the like. EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited to these Examples in any way. Example 1 and Comparative Example 1 Liquid polyisoprene rubber with a molecular weight of 47,000 and a vinyl bond content of 12% and trans-1,4- with a melting point of 60°C
Using polyisoprene (rubber), kneading was performed using a Banbury mixer according to the formulation shown in Table 1. Incidentally, among the compounding materials, the vulcanization accelerator, foaming agent, and foaming aid were added using an open roll after kneading the rubber component using a Banbury mixer. The thus obtained (vulcanized foam) rubber composition was press-vulcanized at 160° C. for 20 minutes to obtain a vulcanized foam. A test piece with a length of 10 cm, a width of 5 cm, and a thickness of 1 cm was cut from the obtained vulcanized foam, heated at 70°C for 2 hours, and the shrinkage rate was determined by comparing the length in the longitudinal direction before and after heating. [(Length in longitudinal direction before heating) -
(Length in the longitudinal direction after heating)]×100/(Length in the longitudinal direction before heating) was determined. For comparison, a foam was obtained from a composition prepared without containing liquid polyisoprene rubber in the same manner as above. When the shrinkage rate of the obtained foam was determined in the same manner as the above method, the results shown in Table 1 were obtained.

【table】

[Table] As shown in Table 1, the foam obtained from the vulcanized foam rubber composition of Example 1 consisting of liquid polyisoprene rubber, trans-1,4-polyisoprene rubber, sulfur, and a blowing agent was Compared to the foam of Comparative Example 1 which does not contain liquid polyisoprene rubber, the shrinkage after heating is significantly smaller. Example 2 and Comparative Example 2 Using liquid polyisoprene rubber with a molecular weight of 29,000 and a vinyl bond content of 14% and 1,2-polybutadiene with a melting point of 80°C, vulcanization and foaming were carried out in the same manner as in Example 1 according to the formulation shown in Table 2. A rubber composition was obtained. The composition was press-vulcanized at 150°C for 15 minutes to obtain a foam. The shrinkage rate of the foam due to heating was determined in the same manner as in Example 1, and the results shown in Table 2 were obtained. On the other hand, for comparison, a composition was prepared in which the above formulation did not contain liquid polyisoprene rubber, and a foam was obtained in the same manner. Table 2 shows the shrinkage rate of the foam upon heating.

【table】

[Table] As shown in Table 2, the foam of Example 2 has a significantly smaller shrinkage rate upon heating than the foam of Comparative Example 2. Comparative Example 3 A liquid polyisoprene with a molecular weight of 29,000 and a vinyl bond content of 14%, cis-1,4-polyisoprene (melting point of about 8°C) and natural rubber were used in the same manner as in Example 1 according to the formulation shown in Table 3. A vulcanized foam rubber composition was obtained. The composition was press-vulcanized at 150° C. for 10 minutes to obtain a foam. When this composition was prepared, when the ingredients were added using an open roll, the adhesion to the roll was very strong and the workability was extremely poor. Furthermore, the foamed product obtained was irregularly foamed and was very soft. Using this foam, shrinkage was measured by the method of Example 1.
It showed a remarkable shrinkage rate of 10.1%.

【table】

【table】

【table】

Claims (1)

[Claims] 1. Vulcanized foam consisting of crystalline trans-1,4-polyisoprene rubber or 1,2-polybutadiene rubber having a melting point of 50 to 110°C, liquid diene rubber, vulcanizing agent, and blowing agent. Rubber composition. 2. The vulcanized foam rubber composition according to claim 1, wherein the liquid diene rubber is a polymer having 35% or less of vinyl bonds and a molecular weight of 6,000 to 100,000. 3. The vulcanized foam rubber composition according to claim 1, wherein the liquid diene rubber is liquid polyisoprene rubber or liquid isoprene-butadiene copolymer rubber.